11/5 Embriology of the Head Flashcards
What is a deffect of nerual tube closure at the head?
Anecephaly
Form most of the facial bones
The neural crest cells
the three origins of the bones of the skull;
The neural crest cells, the paraxial and lateral plate mesoderm.
the part of the skull that arises from the neural crest cells:
the frontal part (frontal; nasal; lacrimal; zygomatic; maxilla; incisive; mandible), the lower sids (Sphen. and Sq. temp.) and the hyoids
what bones are derived from the paraxial mesoderm (somites and somitomeres)
the back of the skull (parietal, pet. temp.; occipitals;)
The somites that provide the paraxial mesoderm for the back of the skull:
occipital somites and somitomeres
arises from a number of paired cartilage elements that fuse and ossify
the base of the skull.
which cartilage elements of the head come from neural crest and which are from paraxial mesoderm?
those in front of the rostral limit of notochord are from n.c. and posterior from paraxial mesoderm.
What etablishes the cranial to caudal segmentation of the pattern of the body?
the Hox code!
How does the cranial to caudel pattern of the somites get carried ventrally?
Migrating crest cells carry segmental information ventrally.
How can we anticipate the related symptoms of a syndrome based on N.C. cells
the structrues produced by crest from the same location can all reflect a common defect.
The Cranial nerve of Brachial arch 1
The Trigeminal nerve (V-3) (mastication); and a little of Geniculate (VII) (facial expression).
The Cranial nerve of Brachial arch 2
CN VII (facial expression), and IX (pharynx and larynx)
what are the minor (2) and major contributor to the head development?
lateral plate mesoderm and the paraxial mesoderm and the N.C. cells
part of the skull that comes from the lateral plate mesoderm
the laryngeals
The Cranial nerve of Brachial arch 3
CN IX (pharynx and larynx)
The Cranial nerve of Brachial arch 4
Vagus (CN X) (pharynx and larynx)
primary contributers to the face from the brachial arches
arches 1 and 2
The bone from the arch 1
(meckel’s cartilage): maxilla, mandible, temporal bone, two middle ear ossicles (malleus, incus)
the bone from the arch 2
(Reichert’s cartilage) one middle ear ossicle (stapes). syloid process, stylohyoid ligament, and lesser horn and part of the body of hyoid
the bone from the arch 3
greater horn and part of body of hyoid
arch 4 bone
thyoid cartilage
arch 6 bone
cricoid cartilage
the origin of the outer ear?
the first and second arch derivatives
how can the outer ear indicate a problem with cranial nerual crest cells)
The same nerual crest cells can that lead to the ear defects also contribute to many other structures (heart inner ear etc.)
What other defects might be suggested by a deformed outer ear?
hearing and cardiac
what is the development of the pinna of the ear?
from the hillocks of the 1st and 2nd arch.
origin of the ear canal
1st cleft
middle ear origin
ossicles from 1st and 2nd arch cartilage
what does the tympanic membrane develop from?
from teh first closing plate
where does the ear develop around in the breachial arches?
around the first pharyngeal cleft and pouch
what does the auditory tube of the middle ear develop from?
1st pouch of the brachial arch.
inner ear origin
from the otic placode that starts as a thickening and then invaginates and makes an otic vesicle
what is the membranous labyrinth of the ear?
semicircular duct and canal and cochlea
what changes the anatomy of the face as the embryo grows?
the growth of the prominences and the merger of some of them
what are the prominances of the face that must grow and merge to make a face?
the single frontal prominence; paired medial nasal prominences; paired lateral nasal prominences; paired maxillary and mandibular prominences!
what do the prominences of the face contribute to?
to the Lower jaw, upper jaw, cheeks, forehead and nose
describe the formation of the face from the merger of the facial prominances
the frontal prominence moves up to form the forehead, the paired medial nasal prominances merge to form the middle of the nose and the philtrum. the lateral nasal folds move with the medial to make the edges of the nose, and merge with the maxillary prominences to form the cheecks. The maxillary prominence merges with the medial nasa prominences just below the nose to complete the upper lip.
How can the growth of the facial prominences give rise to cleft lip or facial cleft?
Cleft lip: maxillary and median nasal prominence mergence failure; Oblique facial cleft: Maxillary and lateral nasal prominence fail to fuse.
How does the palate develop?
outgrowth of palatine shelves around the toungue that reorientate from vertical to horizontal due to growth of mandible and expansion of oral cavity and then fuse at the midline to give a seperate nasal cavity, and the primary palat (the median palatine process, a component of the median nasal process) comes down from the nose to fuse with the palatine shelves (which is the secondary palate.
how do we get different shapes of cleft palate (not just midline)
The primary and secondary palate fuse at a upside down “peace” shape and allow for a number of fusion lines along which a cleft can develop. – Anterior involve the primary and posterior involve the secondary palate
what is the process of tissue that comes down from the front, under the nasal cavity to start to form the palate as a part of the median nasal process.
the primary palate.
the tissue that merge to make the secondary palate
the palatine shelves
what is the origin of the posterior bones of the head?
the somitomeres from the paraxial mesoderm that is just lateral to the neural tube.
what is the difference in a somite and somitomeres
the somitomeres don’t contribute to as much as a somite
what is a somitomere
condensation of paraxial mesoderm
why is it difficult to guess the origin of the muscles and nerves in the face and head
some muscles and nerves come form the same segmental level (arch 2, 3), in other cases (toungue, ocular muslces), the progenitors travel from far away and are innervated by nerves that originate from different embryonic locations
abnormal formation or a birth defect
Dysmorphogenesis
abnormal formation of tissue or organ
malformation
unusual forces distorting a tissue or organ
deformation
tissue or organ breaks down
disruption
cells in tissue or organ are disorganized
dysplasia
types of defects:
isolated or sporadic; “syndromes (cellular or genetic)”, environmental; genetic.
what type of defect is a Craniofacial defects
isolated or sporadic: both environmental and genetic cuases unknown in many cases, defects can occur in a pattern that reflects segmentation.
what are the key indicators or characteristics of craniofacial syndromes:
large involvement of neural crest cells; neural crest cells are highly sensitive to development perturbation; neural crest of the first pharyngeal arch is particulaaryly sensitive (first arch syndrome); can be enviro or genetic
Environmental causes of craniofacial abnormalities example (acne)
Vitamin A exposure craniofacial, outlfow tract defects of the heart and limb defects: microtia (small and low) of the ear; flattened nasal bridge; hypertelorism
Environmental causes of craniofacial abnormalities example (alcohol)
Microcephaly (small head); Epicanthal folds (fold over the corner of the eye like asian eyes); flat midface; indistint philtrum (no groove under the nose)
what is a common cuase of genetic malformation?
problems in the FGF signaling pathway! this could give Craniosynostosis
what is craniosynostosis
different syndromes associated with genetic abnormalities with FGF signalling pathway that give outcomes such as hyper-mandibular growth, eyes too close or too far apart etc.
besides FGF pathway, what is another known genetic cause of craniofacial anomalies?
TCOF1, or a gene that is important for ribosomal biogenesis.
what is hemifacial microsomia or Goldenhar syndrome?
asymmetrically shortened face benign growth of eye or absence of eye and fusion of cervical vertebrae, atresia of an ear and only on one side (one side of the face is unilaterally microtia). higher occurance in gulf war vets.
what is the cause of Digeorge anomaly?
Haploinsufficiency of the DiGeorge Critical region (DGCR; 250 kb – 35-40 genes)
the second most common cause of heart defects:
Digeorge anomaly
What is the facial appearence of diGeorge anomaly
microstomia, small nostrils, small eyes and low-set ears
